The objective of the project is to elucidate the mechanism(s) whereby 1-2 MHz ultrasound perturbs biological systems. The rationale for this objective is that a fundamental mechanistic understanding of the interaction of ultrasound with biological systems will be useful in evaluating the potential impact of ultrasound on human health and safety. The approach of the project involves exposing in vitro single cell or multicell (spheroids) systems to a variety of ultrasound exposure modes selected to enhance or subdue acoustic cavitation. Continuous wave and pulsed ullrasound modes will be analyzed for chemical and biological effectiveness. Theoretical considerations of bubble (transient acoustic cavity) growth, resonance, and collapse will be compared with observations on cavitationally-mediated pertubations to the chemical and biological test systems.